“In-mold molding” means a technology in which, upon performing injection molding of plastics, ceramics or the like, a design-bearing film is interposed inside a mold to transfer an image, a photograph or the like onto a surface of the plastics or the like inside the mold simultaneously with injection molding. “Transfer film for in-mold molding” means a printed film used for an in-mold molding technology to provide a body to be transferred (transfer object) with decoration or other functions by allowing peeling of a transfer layer from a base film to transfer the transfer layer onto to the object. The transfer film for in-mold molding has been widely used for the purpose of decoration and surface protection of a cellular phone terminal, a housing of a laptop computer, a digital camera or the like, other home appliances, a cosmetic container, and also automotive interior and exterior parts.
Simultaneous molding and decoration in which a film is set inside the mold of injection molding includes two techniques, namely in-mold transfer according to which no film remains (no remaining film) in a molded product, and in-mold lamination according which a film remains in the molded product.
Above all, the in-mold transfer does not need a step of preform or trimming that has been complicated in the in-mold lamination because a remaining film is peeled from the molded product after the transfer film is molded and transferred in the in-mold transfer. Therefore, automation and speed increase in decoration and molding steps can be achieved. Further, the in-mold transfer is the technique having a high effect on improvement in productivity and cost reduction to exhibit a strong point in a mass production product in which an economy of scale is required.
The transfer film for in-mold molding is generally composed of a base film, a release layer, a topcoat layer, a printing layer and an adhesive layer, and is peeled on an interface between the release layer and the topcoat layer after injection molding. Therefore, an outermost surface of the molded product is exposed as the topcoat layer, and in order to obtain the molded product having excellent durability, chemical resistance and moldability, a role of the topcoat layer becomes significantly important.
As a method for obtaining the molded product having excellent durability and chemical resistance, a layer formed of an active energy ray-curable resin has been so far used for the topcoat layer.
A method for producing the transfer film for in-mold molding includes a method of irradiating a film with an active energy ray during preparing the film to allow crosslinking and curing (pre-cure) of the active energy ray-curable resin. However, followability of the topcoat layer to the object to be transferred is poor and a crack is easily developed during molding the resin. In order to prevent the crack from being developed, a method has been widely adopted in which no active energy ray is irradiated during preparing the film, and the topcoat layer on the outermost surface is irradiated with the active energy ray to allow crosslinking and curing (after-cure) of the active energy ray-curable resin after the topcoat layer is transferred onto the object to be transferred. However, the method has had a problem as described below.
Upon producing the film, flowability or adhesiveness of the active energy ray-curable resin remains if only a thermally drying step is applied, and during production according to a roll-to-roll system, the method has had such a problem as transferring of the resin onto a guide roll or occurrence of blocking in a winding portion.
Moreover, upon injection of a molding resin or the like into the mold during injection molding, a phenomenon (gate flow) has occurred in several cases in which the topcoat layer, the printing layer or the like near a mold-injecting portion (gate portion) flows out by the resin to be injected.
Furthermore, depending on a mold shape, no followability to a deeply drawn portion has been obtained due to lack of durability of the topcoat layer, and the crack has been developed in several cases.
Moreover, when electrical conductivity is required for the transfer film for in-mold molding, for example, an indium tin oxide (ITO) layer is further laminated thereonto in several cases. However, depending on the mold shape, if in-mold molding is performed by placing inside the mold the transfer film for in-mold molding in which the film has an ITO layer, such a method also has had a problem of break of the ITO layer to cause loss of electrical conductivity.